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Allopatric speciation (from Ancient Greek ἄλλος (állos) 'other' and πατρίς (patrís) 'fatherland') – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model [1]: 86 – is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow.
Ecological speciation can occur pre-zygotically (barriers to reproduction that occur before the formation of a zygote) or post-zygotically (barriers to reproduction that occur after the formation of a zygote). Examples of pre-zygotic isolation include habitat isolation, isolation via pollinator-pollination systems, and
Sympatric speciation is the formation of two or more descendant species from a single ancestral species all occupying the same geographic location. Often-cited examples of sympatric speciation are found in insects that become dependent on different host plants in the same area. [38] [39]
The isolation of two populations of a species due to a change in breeding periods. This isolation acts as a precursor to allochronic speciation, a type of speciation which results when two populations of a species become isolated due to differences in reproductive timing. An example is the periodical 13- and 17-year Magicicada species. [3]
In ecotypes, it is common for continuous, gradual geographic variation to impose analogous phenotypic and genetic variation, a situation which leads to the emergence of clines. [1] A well-known example of a cline is the skin color gradation in indigenous human populations worldwide, which is related to latitude and amounts of sunlight.
Speciation ultimately results due to the reproductive isolation between two populations. This can happen in a multitude of ways, a common mode of which is known as allopatric speciation. The geographic mode, where two species become physically isolated and unable to interbreed, allows for selection to act on both populations independently. Over ...
Geographic and natural elements may likewise add to these cycles and lead to examples of hereditary variety, such as genetic differences that cause genetic isolation. [3] Genetic variations are often unequally distributed over a species' geographic distribution, with differences between populations at the geographic center and the range's ...
The patterns of species distribution across geographical areas can usually be explained through a combination of historical factors such as: speciation, extinction, continental drift, and glaciation. Through observing the geographic distribution of species, we can see associated variations in sea level, river routes, habitat, and river capture.